It is Dayviewer by Total_Noob. A VSH plugin that allows you to display a time string along the top right of your PSP XMB.
I didn't write this, Total_Noob did.
All I did was patch it so that it would work on PSP Go 5.70.
Personally, I find it confusing separating plugins and homebrew because plugins are pieces of homebrew written for the XMB to add extra functionality. It doesn't matter though.
Unfortunately, I cannot redirect anyone to a 5.70 HEN/CFW.
I've always thought of homebrews as games and apps that you would access through the XMB icons menu's like a regular PSP/PS1 game or like Qriosity/Sensme and plugins as something that runs in the background. Which makes them quite different. (Which is why plugins have their own sub forum)
Also, how did you test this to know that it's compatible with the 5.70 firmware on a PSP Go?